Evolution of a predator-prey Volterra-Lotka ecosystem with saturation effect

This paper has studied the evolution of a predator-prey Volterra-Lotka ecosystem with saturation effect for the general case where both predator and prey evolve. We have interesting results under the evolutional condition, as follows: (1) the predator population and the ratio of predator to prey populations increase; (2) the parameters of the prey drift in the direction of increasing multiplication rate and saturation level, while the parameters of the predator drift in the direction of decreasing death rate.     

Enzymatic isomerization and epimerization of D-erythrose 4-phosphate and its quantitative analysis by gas chromatography/mass spectrometry

An enzyme preparation from beef liver catalyzed the isomerization and epimerization of D-erythrose 4-phosphate to D-erythrulose 4-phosphate and D-threose 4-phosphate. The presence of D-erythrulose 4-phosphate and D-threose 4-phosphate was demonstrated by several analytical methods. After dephosphorylation, the presence of D-erythrulose and D-threose was confirmed by thin-layer chromatography, gas-liquid chromatography and an enzymatic method depending upon D-erythrulose reductase. The enzymatic products were also identified and simultaneously quantitated by a new procedure using gas chromatography/mass spectrometry. Each of three tetroses was distinguished by the combination of the reduction with sodium borodeuteride and the determination of relative intensities of the ion pairs m/z 379 and 380 of sugar tetritol trifluoroacetate. By gas chromatography/mass spectrometry, we observed that D-threose 4-phosphate was also converted into D-erythrulose 4-phosphate and D-erythrose 4-phosphate. At the equilibrium, about 90% of the tetrose 4-phosphate existed in the form of D-erythrulose 4-phosphate. On the basis of gas chromatography/mass spectrometric evidence together with gas chromatographic and thin-layer chromatographic patterns, it is suggested that the single enzyme of the beef liver catalyzed both reactions of isomerization and epimerization of aldotetrose 4-phosphate.     

Effects of winter flooding on phosphorus dynamics in rice fields

Limnology - Controlling phosphorous (P) loads from rice fields is important for the conservation of aquatic ecosystems, in part because P is relatively concentrated at its sources. Recently, winter...     

Characterization of translucent segments observed in an smbA mutant of Escherichia coli

Abstract The smbA gene of Escherichia coli is essential for cell proliferation. The smbA2 mutant shows cold-sensitive colony formation at 22°C. A novel morphological phenotype, formation of a translucent segment at midcell or at a cell pole, was observed by phase-contrastt microscopy at a high frequency in the smbA2 mutant cells incubated in L medium lacking NaCl at 22°C, but not observed in L medium containing 1% NaCl or 20% sucrose at the same temperature. No translucent segment was observed in the wild-type cells in any of the media used. Electron microscopic observation revealed that the translucent segments resulted from the enlargement of a periplasmic space by separation of the inner membrane from the peptidoglycan layer and the outer membrane.     

Effect of Osmotic Stress on Turgor Pressure in Mung Bean Root Cells

Turgor pressure in cells of the elongating region of intactmung bean roots was directly measured by using the pressure-probetechnique. After the external osmotic pressure had been increasedfrom 0 MPa to 0.5 MPa, turgor pressure rapidly decreased byabout 0.5 MPa from 0.65 MPa to 0.14 MPa and root elongationstopped. Subsequent turgor regulation was clearly confirmed,which followed the osmotic adjustment to maintain a constantdifference in the osmotic pressure between root-cell sap andthe external medium ( II). It took at least 6 h for turgor pressureto recover to an adjusted constant level of about 0.5 MPa dueto turgor regulation, but rootelongation resumed within onlyan hour after the osmotic treatment. Therefore, the resumptionof root elongation under osmotic stress could not have beendirectly connected with turgor regulation. Furthermore, sincethe amounts of decrease in turgor pressure just after applicationsof various degrees of osmotic stress could be interpreted inrelation to those in II, hydraulic conductivity between theinside and the outside of root cells must be large enough toattain water potential equilibrium rapidly in response to osmoticstress. We conclude that turgor pressure in the cells of theelongating region of mung bean roots is determined mainly by II because of water potential equilibrium. (Received January 27, 1987; Accepted May 21, 1987)     

Formation and maturation of subneural apparatuses at neuromuscular junctions in postnatal rats: a scanning and transmission electron microscopical study

We examined the morphodifferentiation of subneural apparatuses at neuromuscular junctions with scanning and transmission electron microscopy (SEM and TEM) in the sternothyroid muscle of postnatal rats. As evidenced with SEM, primitive synaptic troughs found at birth were smooth cup-like depressions 5-6 micron in diameter. At the 5th postnatal day, low sarcoplasmic ridges appeared in the depression which successively grew and upheaved to remodel the depression into anastomosed gutters during the next 10 days. Subneural apparatuses attained almost the adult form by the 30th day, though synaptic troughs were smaller in size and exhibited a less complex pattern. At birth, the depression contained a few mostly pit-like or elongated oval invaginations:incipient junctional folds. By the 15th day, junctional folds rapidly developed, resulting in about an 18-fold increase in number per endplate with the parallel differentiation of slit-like junctional folds of adult form. At the 30th day, junctional folds were mostly slit-like, though pits still coexisted in a small proportion. As a shape factor, we measured the ratio of the length of the folds to their maximum width (L/W); the folds with L/W less than 2 were defined as pits, those with 2 less than or equal to L/W less than 5 as short slits, and those with L/W greater than or equal to 5 as long slits. At birth, pits occupied about 67% of the total number of the folds per endplate, which decreased to about 14% at the 30th day. Concomitantly, long slits remarkably increased from about 3 to 38%. Short slits increased from about 30 to 50% during the first 10 days but remained almost unchanged thereafter. The maximum L/W ratio was 12 at the 15th day and exceeded 20 after the 30th day. These quantitative data and the finding that pits were often closely associated with each other and also with a slit in a serial fashion indicate that the adjacent pits may fuse to each other and to the preformed slits. With TEM, a few incipient junctional folds were found at the 5th day, which extended into the subneural sarcoplasm with a depth less than 0.4 micron. At the 15th day, junctional folds increased both in number and in the maximum depth of about 0.8 micron. There also occurred a number of basal lamina-containing vacuoles identical in many respects to the transversely sectioned profiles of incipient junctional folds.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of insulin on the glucose utilization in isolated cardiac myocytes from adult rat

The acute effects of insulin on glucose utilization in isolated rat quiescent cardiac myocytes were studied. Insulin (80 nM) increased the rate of glucose clearance by 2-3 times in the presence of glucose ranging from 0.3 microM to 5.5 mM. Glucose transport, which was measured in terms of both D-glucose uptake in the presence of 0.3 microM D-glucose and initial rate of uptake of 3-O-methylglucose, was stimulated 3-fold in the presence of insulin. At higher glucose concentrations (greater than 100 microM), a decrease in glucose clearance rate due to a shift of the rate-limiting step from glucose transport to a post-transport step in the pathway of glucose metabolism was observed. At the physiological concentration of glucose (5.5 mM), about 73% of glucose was metabolized into lactate, about 10% was oxidized into CO2 and the rest (17%) remained inside the cells. The pentose phosphate pathway did not contribute to the glucose metabolism in these cells. Insulin (80 nM) significantly increased the uptake of glucose (112%), and the conversions of glucose into lactate (16%), glycogen (64%), and triglyceride (18%), but not into CO2 (3%). Insulin transiently increased the percentage of I-form of glycogen synthase by 16% above basal, but did not affect the percentage of a-form of glycogen phosphorylase. The content of glucose 6-phosphate in the cells was increased by 46% above the basal value in the presence of insulin. These results indicate that insulin has different acute stimulatory effects on various steps in the metabolic pathway of glucose in isolated quiescent cardiac myocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Kinetic basis for insensitivity to tetrodotoxin and saxitoxin in sodium channels of canine heart and denervated rat skeletal muscle

The single-channel blocking kinetics of tetrodotoxin (TTX), saxitoxin (STX), and several STX derivatives were measured for various Na-channel subtypes incorporated into planar lipid bilayers in the presence of batrachotoxin. The subtypes studied include Na channels from rat skeletal muscle and rat brain, which have high affinity for TTX/STX, and Na channels from denervated rat skeletal muscle and canine heart, which have about 20-60-fold lower affinity for these toxins at 22 degrees C. The equilibrium dissociation constant of toxin binding is an exponential function of voltage (e-fold per 40 mV) in the range of -60 to +60 mV. This voltage dependence is similar for all channel subtypes and toxins, indicating that this property is a conserved feature of channel function for batrachotoxin-activated channels. The decrease in binding affinity for TTX and STX in low-affinity subtypes is due to a 3-9-fold decrease in the association rate constant and a 4-8-fold increase in the dissociation rate constant. For a series of STX derivatives, the association rate constant for toxin binding is approximately an exponential function of net toxin charge in membranes of neutral lipids, implying that there is a negative surface potential due to fixed negative charges in the vicinity of the toxin receptor. The magnitude of this surface potential (-35 to -43 mV at 0.2 M NaCl) is similar for both high- and low-affinity subtypes, suggesting that the lower association rate of toxin binding to toxin-insensitive subtypes is not due to decreased surface charge but rather to a slower protein conformational step. The increased rates of toxin dissociation from insensitive subtypes can be attributed to the loss of a few specific bonding interactions in the binding site such as loss of a hydrogen bond with the N-1 hydroxyl group of neosaxitoxin, which contributes about 1 kcal/mol of intrinsic binding energy.     

Irreversible inhibition of v-src tyrosine kinase activity by herbimycin A and its abrogation by sulfhydryl compounds

Herbimycin A, an antibiotic which reverses Rous sarcoma virus transformation, inhibited irreversibly the auto- and trans-phosphorylation activities of p60v-src in in vitro immune complex kinase assays. The addition of a sulfhydryl compound such as dithiothreitol, 2-mercaptoethanol, glutathione (reduced form) or cysteine abolished the ability of herbimycin A to inactivate p60v-src kinase as well as the ability to reverse transformed cell morphology, whereas the addition of oxidized glutathione, cystine or methionine showed no effect. The sulfhydryl alkylating reagent N-ethylmaleimide also, although less effectively, inactivated p60v-src kinase activity in vitro. These results suggest the likelihood that sulfhydryl groups of p60v-src are involved in the inactivation of v-src tyrosine kinase activity by herbimycin A.